Improved SystemIdExtractor's opened/closed session behavior.

[ Merge of http://go/wvgerrit/201577 ]
[ Cherry-pick of http://ag/28133919 ]

VIC specific: No DRM reprovisioning support

The SystemIdExtractor did not properly define behavior when working
with opened/closed CryptoSessions.  Due to the CryptoSession's class
dual role of being both a session and a general handle into the
crypto engine, small bugs relying on undefined behavior which happened
to return expected output allowed tests to pass.

This CL makes the following changes:
1) Have SystemIdExtractor verify caller expectations when session is
   open.
2) Improved SystemIdExtractor to operate when CryptoSession is opened
   or closed.
3) Updates several SystemIdExtractorTest cases to better test defined
   behavior without relying on undefined behavior.
4) Better code comments; hopefully some which will help prevent future
   misuse of the internal APIs.

Test: system_id_extractor_unittest on Oriole
Test: WVTS on oriole
Bug: 329713288
Change-Id: I65518fe62f43e8060ea752852eb08a3d7132e2a0

libwvdrmengine/cdm/core/include/system_id_extractor.h

@@ -12,6 +12,7 @@ namespace wvutil {
 class FileSystem;
 }  // namespace wvutil
 namespace wvcdm {
+// Forward declarations.
 class CryptoSession;
 class DeviceFiles;
 
@@ -20,6 +21,22 @@ class DeviceFiles;
 // different place.
 class SystemIdExtractor {
  public:
+  // The constructor should be provided all the parameters necessary
+  // to find the system ID.  Although certain provisioning methods
+  // may not use all parameters, this class must behave in a way which
+  // makes it as easy as possible to obtain the system ID, all
+  // parameters are required.
+  //
+  // Parameters:
+  //  |security_level|
+  //    - Requested security level, uses the |crypto_session| handle
+  //      to convert to a concrete security level.
+  //  |crypto_session|
+  //    - Handle into the OEMCrypto platform.  If handle is open,
+  //      then the session's real security level should match
+  //      |security_level|.
+  //  |fs|
+  //    - File system handle to the global file system.
   SystemIdExtractor(RequestedSecurityLevel security_level,
                     CryptoSession* crypto_session, wvutil::FileSystem* fs);
   virtual ~SystemIdExtractor() {}
@@ -30,12 +47,17 @@ class SystemIdExtractor {
   SystemIdExtractor& operator=(const SystemIdExtractor&) = delete;
   SystemIdExtractor& operator=(SystemIdExtractor&&) = delete;
 
+  // Extracts the system ID from the appropriate source.
   virtual bool ExtractSystemId(uint32_t* system_id);
 
   // Extracts the system ID from a keybox key data (aka CA token).
   static bool ExtractSystemIdFromKeyboxData(const std::string& key_data,
                                             uint32_t* system_id);
   // Extracts the system ID from a serialized OEM certificate.
+  // System ID is expected to be in the manufacturer's intermediate
+  // X.509 certificate from the Widevine-defined X.509 v3
+  // Extension found in the TBSCertificate "extensions" attribute.
+  // See RFC 5280 for X.509 certificate structure.
   static bool ExtractSystemIdFromOemCert(const std::string& oem_cert,
                                          uint32_t* system_id);
 
@@ -44,13 +66,15 @@ class SystemIdExtractor {
   }
 
  private:
+  // Note: All the internal ExtractSystemId*() methods assume
+  // |system_id| is not null.
+
   // Extracts the system ID from keybox-based OEMCrypto implementations.
   // System ID is expected to be found in the keybox data.  Devices
   // which require OTA keybox provisioning will return a null system ID.
   bool ExtractSystemIdProv20(uint32_t* system_id);
   // Extracts the system ID from OEM certificate-based OEMCrypto
-  // implementations.  System ID is expected to be in the manufacturers
-  // intermediate X.509 certificate.
+  // implementations.
   bool ExtractSystemIdProv30(uint32_t* system_id);
   // Extracts the system ID from BCC-based OEMCrypto implementations.
   // System ID is expected to be found in the stored OEM certificate
@@ -59,9 +83,20 @@ class SystemIdExtractor {
   // a null system ID.
   bool ExtractSystemIdProv40(uint32_t* system_id);
 
+  // Add future extraction methods here.
+
+  // Verifies that if |crypto_session_| is opened, that the
+  // security level is matches the instances |security_level_|.
+  // If unopened, verifies that |security_level_| is a defined
+  // value.
+  // Returns true if security level is valid, false otherwise.
+  bool VerifySecurityLevelExpectations();
+
   RequestedSecurityLevel security_level_ = kLevelDefault;
   CryptoSession* crypto_session_ = nullptr;
   wvutil::FileSystem* fs_ = nullptr;
+  // Test only handle to DeviceFiles.  When not null, |fs_| will be
+  // ignored.
   DeviceFiles* test_device_files_ = nullptr;
 };
 }  // namespace wvcdm